1. Field of the Invention
This invention relates to a process for preparing low viscosity inorganic filler compound dispersions and to the use of these dispersions in the preparation of polyolefin/inorganic filler compositions.
2. Description of the Prior Art
Much work has been done in the past in the area of preparing filler polyolefin compositions. In the case of highly filled polyolefin compositions, one of the economic limitations on the process is the maximum concentration of inorganic filler compound which can be used and still have the reaction slurry remain stirrable and pumpable. This limitation on the amount of filler dictates a limitation on the amount of product which can be produced in a given piece of equipment. Accordingly, it would be desirable to provide a process in which high concentrations of inorganic filler compound can be dispersed in a suitable diluent without encountering high viscosities.
Prior art processes in which a large amount of filler is present during olefin polymerization include the following:
1. Rine Kruger in U.S. Pat. No. 3,092,438 discloses in Example 4 mixing 100 grams of bentonite, 5 cc of ethylene aluminum sesquibromide and 3.6 cc of tetra-2-ethylhexyl titanate in 500 cc of heptane. The mixture was stirred and propylene gas was bubbled through the solution. This example has been repeated and an increase in viscosity was observed due to the presence of ethylene aluminum sesquibromide.
2. D. F. Herman et al. in U.S. Pat. No. 3,297,466 disclose a continuous process for polymerizing 1-olefins directly onto the surface of various particulate materials. Slurry concentrations up to the pumpable limit are contemplated. The filler is first mixed with the diluent and then pumped through a pipe into which is added a catalytic transition metal compound and a catalytic organometallic reactant.
3. J. A. Orsino et al. in U.S. Pat. No. 3,300,329 disclose in Examples 1, 12, 13, 16, 20 and 21 suspension of large amounts of various particulate metals in a hydrocarbon diluent. Titanium tetrachloride is added, and the reaction is agitated for a period of time. Trialkylaluminum is then added, followed by addition of the olefin.
4. R. J. McManimie in U.S. Pat. No. 3,578,629 discloses in Example 1 the preparation of a catalyst by first reacting titanium tetrachloride and diisobutylaluminum hydride. A large amount of wollastonite is stirred in hexane containing an organosilane coupler compound, and the prereacted catalyst mixture is added to the slurry, followed by the addition of ethylene.